1. Field of the Invention
The present invention generally relates to a liquid crystal display device (LCD). More particularly, the present invention relates to a transmission/reflection combination type LCD capable of providing display in transmission and reflection modes.
2. Description of the Background Art
Liquid crystal display devices (LCDs) are thin, low power consumption display devices. Because of such characteristics, the LCDs are recently used in a variety of applications including office automation (OA) equipments such as word processors and personal computers, portable information equipments such as electronic organizers, and camera-incorporated VTRs (video tape recorders) having a liquid crystal monitor.
These LCDs are roughly divided into two types: reflection type and transmission type. An LCD is not a self-light-emitting display device such as CRT (cathode ray tube) and EL (electroluminescence). In order to provide display, a transmission-type LCD uses light of an illuminating device provided behind a liquid crystal display (LCD) panel (so-called backlight), whereas a reflection-type LCD uses ambient light.
A transmission-type LCD provides display by using light from the backlight. Therefore, display is less susceptible to the brightness of the surrounding environment. As a result, the transmission-type LCD is capable of providing bright display having a high contrast ratio, but has large power consumption due to the backlight. The backlight consumes about 50% or more of the power consumption of a normal transmission-type LCD. Moreover, visibility is reduced if the transmission-type LCD is used in a very bright environment (e.g., outdoor in fine weather). If the luminance of the backlight is increased in order to maintain the visibility, power consumption would further be increased.
On the other hand, a reflection-type LCD does not have a backlight, and therefore has extremely low power consumption. However, the brightness and the contrast ratio of display are significantly affected by the surrounding environment such as brightness in the environment. Especially, visibility is significantly reduced when the reflection-type LCD is used in a dark environment.
In order to solve the above problems, a transmission/reflection combination type LCD capable of providing display in both reflection and transmission modes has been proposed.
The transmission/reflection combination type LCD has a reflecting picture-element electrode (a picture-element electrode which reflects ambient light) and a transmitting picture-element electrode (a picture-element electrode which allows light from the backlight to transmit therethrough) in each picture-element region. Therefore, the transmission/reflection combination type LCD is capable of switching the display mode between the transmission mode and the reflection mode or providing display in both display modes according to the surrounding environment (brightness in the environment). Accordingly, the transmission/reflection combination type LCD has characteristics of both the reflection-type LCD and the transmission-type LCD. In other words, the transmission/reflection combination type LCD has low power consumption, is less affected by brightness in the environment, and is capable of providing bright display with a high contrast ratio. Moreover, the disadvantage of the transmission-type LCD (reduced visibility in a very bright environment (e.g., outdoor in fine weather)) is suppressed.
As described above, the transmission/reflection combination type LCD provides display in a transmission region by using light from the backlight, and provides display in a reflection region by using ambient light. Therefore, if the transmission/reflection combination type LCD has a color filter, the number of times the light passes through the color filter is different between the transmission region and the reflection region. Although the light emitted from the transmission region toward a viewer has passed through the color filter only once, the light emitted from the reflection region toward the viewer has passed through the color filter twice. This makes it difficult to implement bright display with high color purity (excellent color reproduction) in both transmission and reflection regions in the transmission/reflection combination type LCD.
In order to solve the above problem, Japanese Laid-Open Publication No. 2000-111902 discloses an LCD in which a reflection region has a region having no color filter layer.
However, the LCD disclosed in the above Japanese Laid-Open Publication No. 2000-111902 provides display in the reflection region by mixing light passing through the region having the color filter layer and white light passing through the region having no color filter layer. Therefore, although reduction in transmittance in the reflection region is suppressed and light utilization efficiency is improved, color purity of display is not high enough.